1. Field of the Invention
The invention relates to a lift axle suspension having a trailing arm and an inflatable lift bag for raising and lowering the trailing arm in response to the introduction of pressurized air into and exhaustion of pressurized air from the lift bag. In one of its aspects, the invention relates to a reduced weight lift axle suspension having a relatively narrow width trailing arm with an inboard mounted lift bag.
2. Description of the Related Art
Lift axle suspensions are commonly used in semi-tractor/trailer configurations where the varying load of the tractor or trailer can require the need for additional suspensions for distributing the vehicle load over a variable number of ground contact points. Lift axle suspensions typically comprise a pair of trailing arm assemblies between which is supported a vehicle axle with rotatably mounted wheels. Each of the trailing arm assemblies comprises an trailing arm having one end pivotally mounted directly to the vehicle frame or indirectly to the vehicle frame through a frame hanger bracket. Another portion of the trailing arm is connected to the vehicle frame through an air spring.
In previous lift axle suspensions, the trailing arm was typically mounted within the hanger bracket. In these configurations, the lift bag is also mounted within the hanger bracket, resulting in a relatively wide spacing of the hanger bracket plates to accommodate the width of the lift bag, which was typically wider than the trailing arm. The lift bag was mounted between the hanger bracket and the trailing arm but outside the upper rotation limit of the trailing arm to avoid interference with the trailing arm upward movement thereof. The lift bag is thus placed well above the trailing arm.
As a result of the relatively wide dimensions of the hanger bracket, previous trailing arms tended to be designed in a width at least equal to that of the lift bag, which was greater than the width needed for load bearing and other operational parameters. Other suspension components and accessories that interact with the trailing arm were also designed wider and or longer than structurally required to accommodate the extra width of the trailing arm. As a result, these lift axle suspensions tended to be relatively heavy or at least heavier than necessary to carry out the required functions. A reduction in the size and weight of the currently used trailing arm suspensions translates into material cost savings during the construction of the trailing arm assemblies and fuel cost savings during the operation of a vehicle with the lighter trailing arm assembly. More importantly, there is a desire to reduce the weight of current trailing arm assemblies incorporating a lift mechanism.
Additionally, the length of the frame bracket is determined in part by the position of the lift bag in the frame bracket and not necessarily by other features of the suspension. It may be that shorter, and thus lighter, yet of equal strength and function, frame brackets may be achieved without the limitations imposed by an interior-mounted lift bag. Further, the required spacing of the lift bag to avoid the travel of the trailing arm determined the radial distance between the lift bag and the pivot axis of the trailing arm. The greater the radial distance between the lift bag and the pivot axis of the trailing arm, the greater the required elongation of the lift bag to rotate the trailing arm between its retracted and extended positions.
Vehicles with a lift axle suspension have an air pressure system for supplying pressurized air to the air springs, brakes and other accessories. Often an auxiliary air tank, air lines, height control valves, and other air system components are mounted to the frame underneath the vehicle. The sizes of the lift bag and frame bracket limit the available space for these accessories. There is a continuous need for more space to mount the various air system accessories.
According to the invention, a lift axle suspension adapted to be mounted to a vehicle frame for selectively supporting a vehicle frame on an axle with ground engaging wheels comprises a pair of trailing arm assemblies each of which includes a hanger bracket adapted to be mounted to the vehicle frame, a trailing arm pivotally mounted to the hanger bracket for pivotal movement relative to the frame about a pivot axis, a spring operably connecting the trailing arm to the vehicle frame for resisting the pivotal movement of the trailing arm about the pivotal axis toward the frame, an inflatable lift bag operably connecting the trailing arm to the hanger bracket and for selectively raising the trailing arm relative to the frame when the lift bag is inflated and an axle rigidly mounted to the trailing arm. According to the invention, the lift bag is positioned laterally of the hanger bracket, preferably inboard of the hanger bracket and the trailing arm. The hanger bracket is adapted to be mounted to the outboard side of the frame rail. Preferably, the lift bag is laterally spaced from a plane in which the trailing arm pivots.
In one embodiment, the trailing arm comprises a pair of parallel side plates and the hanger bracket fits between the parallel side plates of the trailing arm at the pivot axis. A bushed connector pivotally mounts the pair of parallel side plates of the trailing arm to the hanger bracket.
In a preferred embodiment, the hanger bracket is U-shaped in horizontal cross section and the hanger bracket has a stiffening element mounted within sidewalls of the U-shaped cross section. Further, the hanger bracket tapers from an upper portion toward the trailing arm, and the stiffening element extends in a direction from the frame to the trailing arm.
In a practical embodiment of the invention, a frame bracket is mounted to the hanger bracket and an arm bracket mounted to the trailing arm. The lift bag extends between the frame and arm brackets. The frame bracket is positioned at a lower portion of the hanger bracket and the arm bracket is positioned at an upper portion of the trailing arm. The lift bag has a width greater than a width of the hanger bracket.
In a preferred embodiment of the invention, the pivot axis between the trailing arm and the hanger bracket is between forward and rearward ends of the trailing arm. The axle is mounted rearwardly of the pivot axis and the lift bag is mounted forwardly of the pivot axis. Substantially the entire lift bag is located forwardly of the pivot axis and above the forward end of the trailing arm.
The invention provides an effective lift axle suspension with a relatively low weight because the trailing arm and frame brackets are relatively narrow. Further, the lift bag can be mounted relatively close to the pivot axis without interfering with the movement of the trailing arm and thus has a relatively short extension to raise the trailing arm. Thus, the lift bag can be relatively short and relatively light in weight. The entire suspension forms a relative small package which results in more room beneath the vehicle frame for mounting of other accessories.